Research duo discover first instance of non-human primates whispering to each other

Sep 25, 2013 by Bob Yirka report
A Cotton-top tamarin at Schwerin Zoo. Credit: Harald Hoyer / Wikipedia.

(Phys.org) —Psychology researchers Rachel Morrison and Diana Reiss of The City University of New York have discovered the first instance of non-human primates whispering to one another. In their paper published in Zoo Biology, the two describe how they recorded vocalizations of captive tamarin monkeys and found that when threatened they sometimes revert to whispering to one another to avoid being overheard.

Whispering is a common strategy used by people to communicate with one or more people while simultaneously trying to avoid having others hear. Other animals have been found to lower the volume of their communications as well under certain circumstances, but never before has any other than humans been found to do so. In this new effort, the discovery was inadvertent.

The two researchers were studying cotton-top tamarins at New York's Central Park zoo, hoping to learn more about the kinds of calls the monkeys make to one another under different circumstances. Prior research had found that tamarins are capable of vocalizing a wide range of noises. Morrison and Reiss were most interested in what are known as mobbing calls—sounds members of a group make to confuse or intimidate .

To better understand how the tiny monkeys use mobbing calls, the researchers recorded sounds a group made when a known threat entered the vicinity—a supervisor that had been part of the team that had captured them in the wild. Prior to the study, the monkeys had used mob calls whenever the supervisor came into their view. Neither of the researchers noticed anything unusual as recordings were made, but later during playback analysis they discovered the monkeys were engaging in vocalizations that were at such low amplitude that people in the area couldn't hear them—they were to one another.

The researchers acknowledge that it's impossible to know for sure what exactly the were saying to each other, but it seems pretty clear from observation that they were reminding one another of the threat the man posed and were doing it in a way that wouldn't alert the threat to the calls they were making to each other. The discovery of whispering by a non-human primate, Morrison and Reiss suggest likely means that it occurs in other species as well—researchers just haven't heard them yet.

Explore further: Field study shows titi monkeys convey both location and predator type with vocal alarms

More information: Morrison, R. and Reiss, D. (2013), Whisper-like behavior in a non-human primate. Zoo Biol.. DOI: 10.1002/zoo.21099

Abstract
In humans, whispering has evolved as a counteractive strategy against eavesdropping. Some evidence for whisper-like behavior exists in a few other species, but has not been reported in non-human primates. We discovered the first evidence of whisper-like behavior in a non-human primate, the cotton-top tamarin (Saguinus oedipus), in the course of investigating their use of human-directed mobbing calls. We exposed a family of captive cotton-top tamarins to a supervisor who previously elicited a strong mobbing response. Simultaneous audio–video recordings documented the animals' behavioral and vocal responses in the supervisor's presence and absence. Rather than exhibiting a mobbing response and producing loud human-directed mobbing calls, the tamarins exhibited other anti-predator behaviors and produced low amplitude vocalizations that initially eluded our detection. A post-hoc analysis of the data was conducted to test a new hypothesis—the tamarins were reducing the amplitude of their vocalizations in the context of exposure to a potential threat. Consistent with whisper-like behavior, the amplitude of the tamarins' vocalizations was significantly reduced only in the presence of the supervisor. Due to its subtle properties, this phenomenon may have eluded detection in this species. Increasing evidence of whisper-like behavior in non-human species suggests that such low amplitude signaling may represent a convergence in a communication strategy amongst highly social and cooperative species.

Related Stories

Shout now! How nerve cells initiate voluntary calls

Sep 06, 2013

"Should I say something or not?" Human beings are not alone in pondering this dilemma – animals also face decisions when they communicate by voice. University of Tübingen neurobiologists Dr. Steffen Hage and Professor ...

Island monkeys do not recognize big cat calls

Jan 17, 2008

Monkeys living on an island without big cat predators do not show any particular alarm when recorded tiger growls are played to them, according to research by a UC Davis graduate student. The pig-tailed langurs do, however, ...

I wanna talk like you (oo)

Dec 16, 2011

The role of social structure in animal communication is hotly debated. Non-human primates seem to be born with a range of calls and sounds which is dependent upon their species. But overlying this there seems to be some flexibility ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

Anda
5 / 5 (1) Sep 25, 2013
So, what were they whispering? Have a language???
antialias_physorg
5 / 5 (1) Sep 25, 2013
So, what were they whispering? Have a language???

That's what I was thinking, too. Whispering only makes sense if you know the other party will understand what you are whispering. It doesn't make sense if it's just "some sound" as in a random call.

It does look like some rudimentary language is present. Interesting.
Sean_W
3 / 5 (4) Sep 25, 2013
So, what were they whispering?


***Secrets***

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Making graphene in your kitchen

Graphene has been touted as a wonder material—the world's thinnest substance, but super-strong. Now scientists say it is so easy to make you could produce some in your kitchen.